1. Field of the Invention
This invention is related to a shaft having thermal expansion, thermal pre-load yielding and dynamic pre-load adjusting systems. Particularly, its central shaft will not expand when the temperature arises. It has a partition ring set to yield thermal pre-load. And, it contains a dynamic pre-load adjusting system.
2. Description of the Prior Art
The requirements of manufacturing precision and cutting tool""s rotation speed are higher than before. The major frictions are created from the interface between the shaft and the motor and interface between the shaft and the rotated working object (the bearing is heated due to of pre-load). Under a high speed rotation, the thermal expansion by the bearing and the thermal expansion by the partition ring set are different. In addition, because of their arrangement, they always push each other. Thus, a thermal stress is occurred. Consequently, the frictional force will increase. And, the heat is generated accordingly. Under such thermal expansion effect, the axis of the shaft might be tiled and the protruded length of the shaft could be slightly changed, so that there are some swinging error and protrusion error. As a result, the manufacturing precision is lowered, and the bearing is over-heated. Thus, it will not work properly.
In order to solve the above-mentioned problems, there are some conventional method listed below. However, their disadvantages also can be seen as follows.
1. Shaft with water jacket cooling system:
This is to install a water jacket system around the main shaft as a cooling system. It only can cool the outer surface of the main shaft. It cannot cool down the central shaft portion of the main shaft. However, its cooling efficiency is low. In addition, a cooler or cooling equipment must be used. Therefore, its cost is high, its water temperature cannot be precisely controlled, and the circulated water is hard to be post-processed.
2. Injecting coolant or high pressure air to the central shaft portion:
Because the space around the central shaft inside the main shaft is limited, it is highly difficult to design or install the pipe system for injecting coolant or air. Furthermore, because the central shaft""s rotation speed is very high, the corresponding cooling ability must be very high. For example, it can be enhanced by a compressor or a pump.
3. Variable pre-load mechanism:
By using a hydraulic cylinder, a spring, or piezo-electric element, it can dynamically adjust the applied forces on the inner and outer seat rings of the bearing. However, when the temperature arises, the uncertain factors of thermal expansion and rigidity still exists. Moreover, it might cause oil leakage or poor manufacturing precision, so its reliability is not good.
4. Lubrication:
This is to add some grease, oil-gas mixture or lubricant in the bearings. Although it can reduce the temperature, the reduced range is still quite limited. Particularly, under the high-speed rotation, the lubrication still will cause some serious pollution problem that needs to be solved.
The primary object of the present invention is to provide a shaft having thermal expansion, thermal pre-load yielding and dynamic pre-load adjusting systems. By means of using the central shaft that is made by the zero expansion or very low expansion materials, when the temperature increases, the central shaft will have no thermal expansion effect so as to keep a very high precision.
The next object of the present invention is to provide a shaft having thermal expansion, thermal pre-load yielding and dynamic pre-load adjusting systems. In which, the partition ring set is made of multiple alloys with low and negative thermal expansion coefficients. When the temperature of the partition ring set increases, it reduces the clamping forces between the inner and the outer annular seats of the bearings. Therefore, the frictional force is minimized and the range of increased temperature is limited. By using such the combination of low and negative expansion materials, this invention can automatically achieve the dynamic pre-load adjusting function. So, it will prolong the life of the central shaft and bearings.